Activation of AP-1 and CRE-dependent gene expression via mu-opioid receptor.

Addiction to opiates depend on drug-induced neuroplastic changes and are underlain by alterations of gene expression. Transcription factors Ca2+/cAMP responsive element binding protein (CREB) and activator protein 1 (AP-1) may constitute a direct link between the opioid-regulated signal transduction pathways and modulation of gene expression. Acute treatment of Neuro2a MOR neuroblastoma cells with opioids stimulated CREB activity; prolonged treatment normalized it, while withdrawal from the drug again elicited an increase in phosphorylated CREB levels. Protein kinase C was responsible for the activation of transcription following acute opioid administration whereas the cAMP pathway activated similar mechanisms during withdrawal, making CREB a kind of 'a trigger' reacting to the presence or withdrawal of the opioid signal. Apart from the elevated CREB phosphorylation, CRE binding activity and expression of luciferase reporter gene regulated by CRE elements were increased after single administration and during withdrawal from the prolonged opioid treatment. Along with CREB, AP-1 binding activity and AP-1-directed transcription were stimulated after single administration and during withdrawal from the opioid. These results provide evidence that both single opioid administration and opioid withdrawal activate CREB and CRE-dependent transcriptional mechanisms via distinct intracellular signaling pathways.